Excursion compensation in multipath communication systems with a cyclic prefix

ABSTRACT

Methods, apparatuses, and systems that receive a communication signal. The communication signal may be split into a first communication signal and a second communication signal. The first communication signal may be zero padded. The zero padded first communication signal may be excursion compensated to generate an excursion compensated signal. The excursion compensating may be performed by fast Fourier transform logic. Zero padding may allow for efficient fast Fourier transform process by ensuring that the length of data frames processed is an integer power of two.

This U.S. Patent Application claims priority to U.S. Provisional PatentApplication No. 62/364,714 filed on Jul. 20, 2016 and U.S. patentapplication Ser. No. 15/356,296 filed November 18, 2016, which arehereby incorporated by reference herein in their entireties.

BACKGROUND

Communication systems such as mobile telephone systems, internetconnected computing devices, long distance communication lines,satellite systems, and other systems have had a profound effect on humandevelopment. Communication systems have made the world a smaller placeby allowing people to communicate over great distances with relativeease. Mobile telephone systems have allowed people to be accessible andhave access to data resources around the clock. These systems arerelatively complicated and have many complementary components. Ascommunication systems develop, there are increasing demands that thesystems are designed to operate more efficiently and perform withincreasing effectiveness. For example, mobile phones are expected to beable to transmit more data and have a minimized battery size.

In wireless communication systems, electrical data signals (e.g. voicesignals, internet data, etc.) are transmitted from a transmitter to areceiver using antennas. In order for these electrical data signals tobe propagated as radio waves with adequate strength, prior to theelectrical data signals being propagated by an antenna, the electricaldata signals need to be amplified by an amplifier. Amplifiers,particularly for high performing wireless devices, are relativelyexpensive and sensitive components. Accordingly, when a communicationsystem is designed, cost and operation of an amplifier is carefullyconsidered. For instance, if the amplifiers are too expensive, then acommunication system cannot be constructed that is commercially viable.Likewise, if the amplifiers that are affordable for a communicationsystem have inadequacies, then a communication system may not befunctionally viable. As another example, if amplifiers implemented inbattery operated devices (e.g. mobile telephones) are operated in aninefficient manner, then there may be undesirable battery drain, whichcould as a result undesirably increase the size and/or weight of thebattery operated devices.

In communications systems, a relatively low power communication signalconveying data may be input into an amplifier and the amplifier mayoutput a higher power communication signal. Although the relatively lowpower communication signal is inadequate to create radio waves throughan antenna, the higher power communication signal may be propagatedthrough an antenna so that communication is possible between twowireless devices. However, if the relatively low power communicationsignal input into the amplifier is too high, the amplifier will notoperate properly, causing problems such as distortions or interference.If the relatively low power communication signals are too low, link datacapacity is reduced or amplifier power efficiency may be non-optimal.Accordingly, in order to maximize the utility of an amplifier, the lowpower communication signal input into the amplifier should be as strongas possible relative to the signal magnitude threshold of an amplifierwithout the relatively low power communication signals exceeding thesignal magnitude threshold of the amplifier. The signal magnitudethreshold of an amplifier is related to the maximum signal strength thatan amplifier can receive without causing distortions or interference.

Portions of the relatively low input communication signal input into anamplifier whose magnitude exceeds the signal magnitude threshold may bereferred to as excursions. These excursions can be suppressed, thusallowing an amplifier to operate without distortions or interference orin an optimal power efficient manner. However, when these excursions aresuppressed without frequency domain considerations, random noise atunacceptable levels may be introduced into the communication signal,which can unacceptably increase the rate of bit errors over thecommunication link. Many communication systems (e.g. LTE mobile phonecommunication systems) have performance requirements parameters, whichconstrain noise levels below certain levels relative to associatedsignal power. Accordingly, when excursions are suppressed, then theseperformance requirements parameters must also be satisfied.

Some communications systems are multipath communication systems where atransmitter has multiple antennas and a receiver has multiple antennas,which transmit and receive the same frequencies. Normally, competingsignals transmitted and received using the same frequencies suffer fromdestructive interference. However, in multiple-in multiple-out (MIMO)communication systems or other multipath communication signals, theparallel signals can be strategically mixed together to manipulate themultipath radio environment. These mixed signals also have the challengethat they should not have excursions which exceed the signal magnitudethresholds of the associated amplifiers. Since these MIMO communicationsignals are a strategic mix of communication signals which may havedifferent performance requirements parameters, it is a substantialchallenge to compensate for these excursions while at the same timesatisfying the performance requirements parameters of the communicationsystem.

In some communication systems, cyclic prefixes are used in conjunctionwith modulation in order to retain sinusoids' properties in multipathchannels. Sinusoidal signals are eigenfunctions of linear andtime-invariant systems. Therefore, if the channel is assumed to belinear and time-invariant, then a sinusoid of infinite duration would bean eigenfunction. However, in practice, this cannot be achieved, as realsignals are always time-limited. So, to mimic the infinite behavior,prefixing the end of the symbol to the beginning makes the linearconvolution of the channel appear as though it were circularconvolution, and thus, preserve this property in the part of the symbolafter the cyclic prefix. However, there are challenges in communicationsystems that used cyclic prefixes in conjunction with excursioncompensation.

SUMMARY

Embodiments relate to a method and/or apparatus that receives acommunication signal. The communication signal may be split into a firstcommunication signal and a second communication signal. The firstcommunication signal may be zero padded. The zero padded firstcommunication signal may be excursion compensated to generate anexcursion compensated signal. The excursion compensating may beperformed by fast Fourier transform logic. Zero padding and/orcalculated interpolation may allow for efficient fast Fourier transformprocess by ensuring that the length of data frames processed is aninteger power of two. In embodiments, zero padding and/or interpolationmay accommodate for complexities due to the use of cyclic prefixes incommunication systems that implement excursion compensation.

DRAWINGS

Example FIG. 1 illustrates a communications network, in accordance withembodiments.

Example FIGS. 2A through 2B illustrate radios in wireless communication,in accordance with embodiments.

Example FIG. 3 illustrates simplified aspects of a multi-antenna basestation, in accordance with embodiments.

Example FIGS. 4A through 4D illustrate transmitters, in accordance withembodiments.

Example FIGS. 5A through 5C illustrates an excursion compensation unit,in accordance with embodiments.

Example FIGS. 6A through 6C illustrate time domain transmission signalsthat are excursion compensated at a multi-antenna transmitter, inaccordance with embodiments.

Example FIGS. 7A through 7C illustrate frequency domain signals that aresubject to excursion compensation processing at a multi-antennatransmitter, in accordance with embodiments.

Example FIGS. 8A through 8G illustrate a frequency domain scaling unitin relation to a zero padding unit and a tail compensation unit, inaccordance with embodiments.

Example FIGS. 9A through 9H illustrate a frequency domain scaling unitin relation to an interpolation unit and a decimation unit, inaccordance with embodiments.

DESCRIPTION

Example FIG. 1 illustrates a communications network 10, in accordancewith embodiments. Communications network 10 may be a wireless network,although embodiments are not limited to wireless networks. Thecommunications network 10 illustrated in FIG. 1 is merely exemplary forillustrative purposes and is not intended to limit embodiments.Communications network 10 may be a mobile telephone network thatservices mobile phones 12 a, 12 b, 14 a, and 14 b. Mobile phones 12 aand 12 b may be in wireless communication with base station 18.Likewise, mobile phones 14 a and 14 b may be in wireless communicationwith base station 20. Base station 18 and base station 20 may be coupledto network 16, which may be a wired network, optical network, wirelessnetwork, or any other communication network as is appreciated by thoseof ordinary skill in the art. Other communication devices (e.g.computers, landline telephones, servers, data centers, etc.) may becoupled to network 16, as is appreciated by those of ordinary skill inthe art.

In embodiments, by wireless communication between mobile phones 12 a, 12b, 14 a, and 14 b with base stations 18 and 20, mobile phones 12 a, 12b, 14 a, and 14 b may have access to network 16 and any resourcescoupled to network 16. For example, resources coupled to network 16 mayinclude voice communications and/or data communications as isappreciated by those of ordinary skill in the art. Communication betweenmobile phones 12 a, 12 b, 14 a, and 14 b with base stations 18 and 20may be engineered for communication reliability and/or efficiency.

Example FIGS. 2A through 2B illustrate radios in wireless communication,in accordance with embodiments. In embodiments, power amplifiers aresensitive components which consume a significant amount of electricalpower. Preservation, efficiency, and/or management of power amplifierpower consumption is imperative when engineering wireless communicationsystems.

Example FIG. 2A illustrates first radio 13 and second radio 15 in radiocommunication between respective antennas 22 and 24, in accordance withembodiments. Antenna 22 of first radio 13 is coupled to power amplifier17. Power amplifier may be a critical component of first radio 13 and asubstantial source of power drain during operation of first radio 13.Likewise second radio 15 may have an associated power amplifier 19 fortransmission of wireless signals, in accordance with embodiments.

Example FIG. 2B illustrates base station 18 in wireless communicationwith mobile phone 12, in accordance with embodiments. In embodiments,base station 18 and mobile phone 12 may be wirelessly communicating in along-term evolution (LTE) communication system implementing multiple-inmultiple-out (MIMO) configurations. For example, an LTE communicationsystem implementing MIMO may be configured to have four antennas 22 athrough 22 d at base station 18 and two antennas 24 a and 24 b at mobilephone 12. One of ordinary skill in the art will appreciate thatembodiments may be implemented in other MIMO communication systems ormultipath communication systems that utilize any number of antennas at atransmitter (e.g. base station 18) and any number of antennas at areceiver (e.g. mobile phone 12). One of ordinary skill in the art wouldappreciate that embodiments are not limited to a mobile telephonecommunication system, base stations, and/or mobile phones. Base station18 and mobile phone 12 are merely examples of devices that includetransmitters and receivers. However, for the simplicity of illustration,the following detailed description uses mobile phones and base stationswith arbitrary number of antennas as illustrative examples withoutlimiting the scope of the embodiments to other communication systems.

As illustrated in example FIG. 2B, there are two wireless paths fromantenna 22 a of the base station 18 to antennas 24 a and 24 b of mobilephone 12. Likewise, there are multiple paths from each of antennas 22 b,22 c, and 22 d of base station to antennas 24 a and 24 b of mobile phone12. Although these wireless paths are illustrated as direct wirelesspaths, those skilled in the art appreciate that these paths may beindirect (e.g. reflecting off of items in the surrounding environmentsuch as buildings, geography, vehicles, people, etc.). Further, sinceall of the wireless paths illustrated between base station 18 and mobilephone 12 are transmitting the same band of frequencies, there isinterference between the multiple wireless signals. As those of ordinaryskill in the art appreciate, since MIMO communication systemsselectively precode the wireless signals that travel by the multiplewireless paths between base station 18 and mobile phone 12, destructiveinterference between the multiple wireless signals may be minimizedand/or otherwise manipulated.

Example FIG. 3 illustrates simplified aspects of base station 18 thatare necessary for transmission of communication signals, in accordancewith embodiments. Base station 18 may include data processor 26 andtransmitter 28. Data processor 26 may receive data from network 16 andorganize the received data to provide data streams to transmitter 28.For example, base station 18 may service a plurality of mobile phones ina cell of a wireless communication network. Data processor 26 mayreceive data to be communicated to the plurality of mobile phone andarrange the data into data streams to be transmitted by transmitter 28.For simplicity of illustration, data processor 26 may perform data layerprocessing for base station 18 and transmitter 28 may perform physicallayer processing for base station 18. However, in embodiments, dataprocessor 26 may also perform physical layer processing or transmitter28 may also perform data layer processing, as the functions of dataprocessor 26 and transmitter 28 may be intertwined. Transmitter 28 mayprovide electrical signals to antennas 22 a through 22 d for MIMOcommunication. Although example FIG. 3 illustrates aspects of basestation 18, these aspects (e.g. data processor 26 and transmitter 28)are also applicable to any other kind of communication device.

Example FIGS. 4A through 4D illustrate transmitters, in accordance withembodiments.

Example FIG. 4A illustrates transmitter 28, in accordance withembodiments. Transmitter 28 may include an encoder and/or modulator unit30 which encodes and modulates data signals input into transmitter 28. Amodulated signal output from encoder/modulator 30 may be extended byadding a cyclic prefix in cyclic prefix unit 31, in accordance withembodiments. A modulated signal with cyclic prefix may be output fromcyclic prefix unit 31, in accordance with embodiments. Excursioncompensation unit 36 excursion compensates a modulated signal withcyclic prefix prior to amplification and transmission by amplifier 38and antenna 22, in accordance with embodiments. In embodiments,excursion compensation unit 36 comprises fast Fourier transformalgorithms to excursion compensate a modulated signal with cyclicprefix. In embodiments, since fast Fourier transform algorithms are mostenergy-efficient when transforming vectors having length equal to aninteger power of two, excursion compensation unit 36 may zero pad amodulated signal with cyclic prefix in order to implement an efficientalgorithm, thus conserving computational and/or power resources. Inembodiments, since fast Fourier transform algorithms are mostenergy-efficient when transforming vectors having length equal to aninteger power of two, excursion compensation unit 36 may selectivelyinterpolate a modulated signal with cyclic prefix in order to implementan efficient algorithm, thus conserving computational and/or powerresources.

Example FIG. 4B illustrates transmitter 28 with fast Fourier transform(FFT) and inverse fast Fourier transform (IFFT) computation units (e.g.L-point IFFT 35, K-point FFT 33, and K-point IFFT 37), in accordancewith embodiments. Cyclic prefix unit 31 is optional and excluded forefficiency. Encoder/modulator 30 may include L-point IFFT computationunit 35 based frame lengths of a communication signal (e.g. OFDMA and/orSC-FDMA communication signals). In embodiments, K-point FFT 33 ofexcursion compensation unit 36 may be twice the length of L-point IFFTto accommodate for a cyclic prefix length added to the signal afterbeing encoded and/or modulated by encoder modulator 30. Likewise,K-point IFFT 37 of FIG. 4B may optionally be a 2L-point IFFT 37 in FIG.4C, in accordance with embodiments. Accordingly, example FIG. 4Cillustrates a FFT computation at 2L-point FFT 33 and 2L-point IFFT 37that are twice the length of L-point IFFT 35, in accordance withembodiments.

Example FIG. 4D illustrates transmitter 28, which may be implemented inany multi-antenna wireless device, in accordance with embodiments. Datastreams may be received by transmitter 28 in a variety of forms. Forexample, data streams input into transmitter 28 may be the output of ademultiplexer that divides a single higher bit rate data stream into aplurality of lower bit rate data streams. In embodiments, thedemultiplexing of data streams may be performed inside transmitter 28 oroutside of transmitter 28 without departing from embodiments. Forillustrative purposes, transmitter 28 is shown receiving multiple datastreams, although in configurations the multiple data streams could begenerated inside transmitter 28 without departing from the scope ofembodiments. As examples, data streams input into transmitter 28 may bea plurality of different data streams from different sources and/or be aproduct of a demultiplexed higher bit rate data stream into a pluralityof lower bit rate data streams, as appreciated by those of ordinaryskill in the art. The number of data streams input into transmitter 28may equal the number of antennas 22 a through 22 d used by transmitter28.

In embodiments, each of the data streams input into transmitter 28 maybe encoded and/or modulated by encoders/modulators 30 a through 30 d.Embodiments are not limited to any specific number of encoders ormodulators, although the number of encoders or modulators may match thenumber of antennas 22 a through 22 d used by transmitter 28. Forillustrative purposes, FIG. 4D illustrates four sets ofencoder/modulators 30 a through 30 d associated with four antennas 22 athrough 22 d of transmitter 28 (e.g. a four antenna MIMO base station).

In embodiments, encoders/modulators 30 a through 30 d may each includean encoder. An encoder may be a device, circuit, transducer, softwareprogram, algorithm, and/or combination thereof that convert informationfrom one format or code to another for the purposes of standardization,speed, bit-error mitigation and/or compression. For the purposes ofillustration, encoders of encoders/modulators 30 a through 30 d areillustrated as part of transmitter 28. Encoder functionality may beincluded in data processor 26, as appreciated by one of ordinary skillin the art. One of ordinary skill in the art would appreciate thatencoding of data may be implemented in a variety of ways prior to theencoded data being modulated and may be implemented through a pluralityof processes. In embodiments, some of the encoding of data may beimplemented in an encoder and some of the encoding of data may beimplemented in a modulator. One of ordinary skill in the art wouldappreciate that encoding may be performed separate or in conjunctionwith modulation without departing from the scope of embodiments.

In embodiments, encoders/modulators 30 a through 30 d may each include amodulator. A modulator may vary one or more properties of a signal withinformation from input information signals. Information signals inputinto encoders/modulators 30 a through 30 d may encode and modulate thedata streams into a plurality of subchannels that are frequency divisionmultiplexed. For example, in LTE wireless communication systems,downlink subchannels (e.g. communication signals from base station 18 tomobile phone 12) may be modulated using orthogonal frequency divisionmultiple access (OFDMA), while uplink subchannels (e.g. communicationsignals from mobile phone 12 to base state 28) may be modulated usingsingle carrier frequency division multiple access (SC-FDMA). However,OFDMA and SC-FDMA are just two examples of a frequency divisionmultiplexed modulation methods that modulate information signals into aplurality of frequency distinguishable subchannels. Embodiments relateto any communication system that implements subchannels duringmodulation. Embodiments may be implemented in Wi-Fi wirelesscommunication systems, WiMAX wireless communication systems, HSPA+wireless communication systems, or any other wireless communicationsystem, wired communication system, or optical communication system thatmanipulates multipath propagation of communication signals.

Encoders/modulators 30 a through 30 d may output a plurality ofcommunication signals to cyclic prefix units 31 a through 31 d, inaccordance with embodiments. Cyclic prefix units 31 a through 31 d mayadd cyclic prefixes to communication signals output fromencoder/modulators 30 a through 30 d. In embodiments, encoder/modulators30 a through 30 d may have different parameters based on modulationand/or encoding applied.

Cyclic prefix units 31 a through 31 d may output a plurality ofcommunication signals to precoder 32, where each of these communicationsignals includes a plurality of frequency distinguishable sub channels.Although encoders/modulators 30 a through 30 d may be functionallyand/or effectively separate from each other, precoder 32 implementsprecoding algorithms to each of the signals input into precoder 32 fromencoders/modulators 30 a through 30 d that effectively mixes thesesignals in a manner that is responsive to propagation channel multi-pathcharacteristics. In each of encoders/modulators 30 a through 30 d, theplurality of communication signals may each be modulated into aplurality of frequency domain subchannels, with each subchannel havingits own frequency spectrum. For example, in LTE communication systems,downlink communication signals may be modulated using orthogonalfrequency division multiple access (OFMDA) with a plurality of parallelsubchannels distinguishable by their frequency. Likewise, in LTEcommunication systems, uplink communication signals may be modulatedusing single carrier frequency division multiple access (SC-FDMA) alsowith a plurality of parallel subchannels distinguishable by theirfrequency.

Each of the individual frequency domain subchannels comprising each ofthe time domain communication signals input into precoder 32 may haveits own performance requirements parameters. As appreciated by thoseskilled in the art, performance requirement parameters may vary from onecommunication symbol (e.g. a frequency division multiplexed symbol) tothe next, reflecting different combinations of modulation and coding ineach subchannel. For example, in LTE wireless communication systems,error vector magnitude (EVM) specifications may dictate performance of adigital radio transmitter or receiver. Noise, distortion, spurioussignals, and/or phase noise all degrade performance of a digital radiotransmitter or receiver. The EVM specification constrains the short-termaverage ratio of the composite noise to signal power, as measured in thecorresponding subchannel at the receiver, to be less than or equal tothe EVM specified value. System operators and equipment manufacturersset performance requirements parameters (e.g. EVM specifications in LTEcommunication systems) in order to qualify equipment (e.g. base stationsand mobile phones) which may be used on a network. Specifically, EVMspecifications provide a comprehensive measure of the quality of theradio transmitter for use in digital communications. Since wirelessnetworks should be designed to operate in predictable and dependableways, quality standards (e.g. performance requirements parameters)should be implemented for network quality control purposes. Wirelessservice providers and wireless equipment manufacturers should only useequipment that satisfies performance requirements parameters, sincethese performance requirements parameters are central to the overallcommunication network design and/or dependability of a network tocustomers.

Particular to MIMO communication systems or other multipathcommunication systems, each of the encoders/modulators 30 a through 30 dmay have the same set of frequency distinguishable subchannels that willultimately be transmitted at the same time from antennas 22 a through 22d. For example, a subchannel modulated at frequency ƒ_(n) in each ofencoders/modulators 30 a through 30 d may be transmitted throughantennas 22 a through 22 d at the same time. In order to avoiddestructive interference at frequency ƒ_(n), precoder 32 selectivelymixes each of the subchannels modulated at frequency ƒ_(n) such thateach of the signals transmitted from antennas 22 through 22 d atfrequency ƒ_(n) do not cumulatively destructively interfere with eachother in their receiver outputs. Without precoding performed in precoder32, the parallel subchannels modulated at ƒ_(n) by encoders/modulators30 a through 30 d would destructively interfere with each other and awireless communication link could not be practically established.However, through the precoding performed by precoder 32, the multipathcharacteristics may be manipulated such that destructive interference isnot only avoided, but the multipath characteristics of the wirelessenvironment are exploited to increase the amount of data that can bewirelessly communicated between a transmitter (e.g. base station 18) andreceiver (e.g. mobile phone 12) that both have multiple antennas.

However, each of the subchannels at frequency ƒ_(n) output fromencoders/modulators 30 a through 30 d and input into precoder 32 mayhave different performance requirements parameters. For instance, aspecific subchannel of the encoded/modulated signal output fromencoder/modulator 30 a may have been subjected to QPSK modulation, whilethe corresponding subchannel of the encoded/modulated signal output fromencoder/modulator 30 b may have been subjected to 16-QAM modulation,which may each have different performance requirements parameters (e.g.EVM specifications) in an LTE communication system. Accordingly, eachcommunication signal output from precoder 32 into excursion compensationunits 36 a through 36 d may have a mix of performance requirementsparameters in each signal. In embodiments, excursion compensation units36 a through 36 d may be configured to maximize the efficiency ofamplifiers 38 a through 38 d.

In a MIMO communication system, precoder 32 may selectively modify orprecode the plurality of communication signals to generate a pluralityof parallel precoded communication signals. Each of these parallelprecoded communication signals will be a selective mix of all of thecommunication signals output from encoders/modulators 30 a through 30 d.The selective precoding of the plurality of communication signalsexploit multipath propagation from a plurality of antennas of atransmitter (e.g. antennas 22 a through 22 d) to a plurality of antennasat a receiver (e.g. antennas 24 a and 24 b of mobile phone 12illustrated in FIG. 2A). Ordinarily, transmitting a plurality of datasignals simultaneously on overlapping radio frequency spectrums wouldcause destructive interference between the subchannels that degradewireless communication performance. However, in MIMO or other multipathcommunication systems, by selectively precoding the communicationsignals at precoder 32, beamforming and/or diversity characteristics maybe manipulated to increase the overall wireless communication capacityand/or efficiency. For this reason, LTE communication systems requireMIMO communication between base stations 18 and 20 and mobile phones 12a, 12 b, 14 a, and 14 b, which relates to non-limiting exampleembodiments.

Example FIGS. 5A through 5C illustrates an excursion compensation unit,in accordance with embodiments.

Example FIG. 5A illustrates an excursion compensation unit 36, inaccordance with embodiments. As an illustrative example, the time domainprecoded communication signal input into excursion compensation unit 36may have a time domain waveform 40 (whose magnitude is illustrated inexample FIG. 6A) with a portion of its magnitude greater than the signalmagnitude threshold 42 of one of the associated amplifiers 38 a through38 d. The time domain precoded communication signal 40 is initiallysplit in excursion compensation unit 36 into a first precodedcommunication signal 41 and a second precoded communication signal 43.

The first precoded communication signal 41 is delayed by delay element56, while the second precoded communication 43 signal is processed bytime domain excursion generation unit 58 and frequency domain scalingunit 60. Following necessary filtering and scaling operations on thesecond precoded communication signal 43, an excursion signal derivedfrom the second precoded communication signal 43 may ultimately besubtracted from the first precoded communication signal 41 to generatean excursion compensated precoded communication signal 45 (whosemagnitude is illustrated as example waveform 46 in FIG. 6C) which isoutput from the excursion compensation unit 36. Delay element 56 may beimplemented by any process and/or device appreciated by those skilled inthe art. The purpose of delay element 56 is to allow time for the secondprecoded communication 43 signal to be processed by time domainexcursion generation unit 58 and frequency domain scaling unit 60. Sincea generated excursion signal may be subtracted from the first precodedcommunication signal 41 in synchronization to generate excursioncompensated communication signal 45, delay element 56 allows for thissynchronization. Since the required processing is accomplished in afixed amount of time by the time domain excursion generating unit 58 andfrequency domain scaling unit 60, only a constant amount of delay isrequired to maintain time alignment between the two inputs tosubtraction operation 62.

The second precoded communication signal 43 (whose magnitude isillustrated as example waveform 40 in FIG. 6A) is input into time domainexcursion generation unit 58. Time domain excursion generation unit 58extracts in the time domain the portion of the second precodedcommunication signal 43 whose magnitude is above the signal magnitudethreshold of the associated with amplifiers 38 to generate time domainexcursion signal (whose magnitude is illustrated as example waveform 44in FIG. 6B). This time domain excursion signal may ultimately besubtracted from the first precoded communication signal 40 afterfiltering (to comply with regulatory constraints on power outside thesignal bandwidth) and frequency domain channel scaling in frequencydomain scaling unit 60 to generate excursion compensated precodedcommunication signal 45 whose magnitude lies below the signal magnitudethreshold 42 of the associated amplifier (illustrated as examplewaveform 46 in FIG. 6C). In embodiments, a time-domain scaling operationis performed prior to a frequency domain scaling operation.

Extracted excursion signal (whose magnitude is illustrated as examplewaveform 44 in FIG. 6B) output from time domain excursion generationunit 58 is input into frequency domain scaling unit 60. In frequencydomain scaling unit 60, an extracted excursion signal (whose magnitudeis illustrated as example waveform 44 in FIG. 6B) is converted to thefrequency domain excursion signal (illustrated as example frequencyspectrum 50 in example FIG. 7A). The frequency domain excursion signal(e.g. frequency spectrum 50) is scaled in the frequency domain togenerate scaled frequency domain signals (illustrated as examplesubchannels 54 a through 54 h in FIG. 7C). The scaling of the scaledfrequency domain excursion signals (illustrated as example subchannels54 a through 54 h in FIG. 7C) are scaled according to performancerequirements parameters of the communication signal. The scaledfrequency domain signals (illustrated as example subchannels 54 athrough 54 h in FIG. 7C) are then converted back into the time domain togenerate a time domain signal whose magnitude exhibits a substantiallysimilar shape as the magnitude of the extracted excursion signal (asillustrated by example waveform 44 in example FIG. 6B). Although theremay be distorted differences between extracted excursion signal (whosemagnitude is illustrated by example waveform 44 in example FIG. 6B)before and after the time domain excursion extraction and the frequencydomain channel scaling, extracted excursion signals may havesubstantially the same complex shape before and after frequency domainchannel scaling, since it is to be subtracted in the time domain fromthe first precoded communication signal 41 by subtraction operation 62such that the scaled precoded communication signal 45 is less than thesignal magnitude threshold 42 of the associated amplifier.

Example FIG. 5B illustrates excursion compensation unit 36, inaccordance with embodiments. A zero padding unit 59 modifies the signaloutput from time domain excursion generation unit 58 which allow forefficient computational processing in frequency domain scaling unit 60.For example, zero padding unit 59 may add zero and/or nominal entries ina frame length, such that the FFT and IFFT processing in frequencydomain scaling unit 60 is computationally efficient, in accordance withembodiments. In embodiments, zero padding unit 59 may zero pad a selectnumber of entries such that the FFT and IFFT computations in frequencydomain scaling unit 60 perform computations on frames that have a lengththat is an integer power of two. After a zero padded signal is processedin frequency domain scaling unit 60, tail compensation unit 61 maycompensate for the zero padding unit 59 by discarding entries that werezero padded, so that signal 49 and signal D41 are synchronized and havethe same frame length, in accordance with embodiments.

Example FIG. 5C illustrates excursion compensation unit 36, inaccordance with embodiments. In embodiments, an interpolation unit 63may process the signal output from time domain excursion generation unit58 such that the frame length output from interpolation unit 63 allowsfor efficient computational processing in frequency domain scaling unit.In embodiments, interpolation unit 63 may interpolate the signal suchthat the frames output from interpolation unit 63 have a length that isan integer power of two. After an interpolated signal is processed infrequency domain scaling unit 60, decimation unit 65 may decimate thesignal such that the signal 49 has the same number of frame entries assignal D41.

In embodiments illustrated in FIGS. 5B and 5C, zero padding unit 59and/or interpolation unit 63 may be necessitated because cyclic prefixunit(s) 31 increase the frame length of a signal from that output fromencoder/modulator(s) 30 to have a length that is not an integer power oftwo. In embodiments, in order for frequency domain scaling unit 60 to beefficiently implemented, it should include FFT or IFFT algorithms whichprocess frame lengths that have a length equal to an integer power oftwo. Since cyclic prefix unit(s) 31 often do not increase the length ofa frame output from encoder/modulator(s) 30 by more than the length ofone frame, embodiments implement FFT and IFFT algorithms with framelengths twice as long as FFT and/or IFFT algorithms used inencoder/modulator(s) 30.

Example FIGS. 6A through 6C illustrate time domain transmission signalsthat are excursion compensated at a multi-antenna transmitter, inaccordance with embodiments.

Example FIG. 6A illustrates the magnitude over time of an exampleprecoded communication signal 40 output from precoder 32 and input intoone of excursion compensation units 36 a, 36 b, 36 c, or 36 d. Thisexample precoded communication signal 40, shown in the time domain,corresponds to a plurality of frequency domain subchannels which weremodulated by encoder/modulator 30 a, 30 b, 30 c, or 30 d and mixedtogether in precoder 32. A signal magnitude threshold 42 ofcorresponding amplifier 38 a, 38 b, 38 c, or 38 d indicates the maximumsignal magnitude that the amplifier 38 a, 38 b, 38 c, or 38 d can handlewithout exhibiting frequency domain aberrations and/or operatinginefficiently. The portion of this precoded communication signal 40whose magnitude exceeds the signal magnitude threshold of thecorresponding amplifier 38 a, 38 b, 38 c, or 38 d is an excursionportion of the precoded communication signal 40. Excursion compensationunits 36 a through 36 d are configured to modify the precodedcommunication signals output from precoder 32 such that the excursioncompensated precoded communication signals have a signal magnitude belowthe signal magnitude threshold level 42 of the corresponding amplifiers38 a through 38 d. For example, a precoded communication signal 40output from precoder 32 (whose magnitude is illustrated in FIG. 6A) maybe excursion compensated in excursion compensation unit 36 a to outputexcursion compensated precoded communication signal 46 (whose magnitudeis illustrated in FIG. 6C). As illustrated in example FIG. 6C, since themagnitude of the excursion compensated precoded communication signal 46is below the signal magnitude threshold 42 of the correspondingamplifier, the corresponding amplifier will be able to operate properlyand/or operate without costly backoff.

However, when a precoded communication signal output from precoder 32 isexcursion compensated by one of excursion compensation units 36 athrough 36 d, noise is inevitably introduced to the subchannels in thefrequency domain. This introduced noise cannot exceed the performancerequirements parameters of the communication system (e.g. EVMspecifications of an LTE communication system, regulatory spectral masksconstraining out-of-band transmission energy, etc.). Accordingly, it isnot a simple matter of clipping the precoded communication signal 40(whose magnitude is illustrated in FIG. 6A) in the time domain toproduce the excursion compensated precoded signal 46 (whose magnitude isillustrated in FIG. 6C). Since the excursion compensated precodedcommunication signals are amplified by amplifier 38 a through 38 d andthen propagated by antennas 22 a through 22 d into a multipath radioenvironment where there is interference between the subchannelfrequencies, the excursion compensation must accommodate for themultipath interference such that the communication signals reconstructedat the receiver after post processing do not have noise that exceeds theperformance requirements of the communication system. That is, thecomposite noise due to excursion compensation at the input to anyreceiver demodulator/decoder includes a mixture of excursion noisecontributions from the plurality of transmitter excursions. Inembodiments, the excursion compensation units 36 a through 36 d mustcompensate for excursions in the time domain such that the signalmagnitude is not greater than the signal magnitude threshold of theassociated amplifiers 38 a through 38 d and also compensate in thefrequency domain such that the subchannels satisfy the performancerequirements parameters notwithstanding the multipath interference ofsubchannels propagated at the same frequency from the different antennas22 a through 22 d.

Excursion compensation units 36 a through 36 d should suppressexcursions above the signal magnitude threshold of the associatedamplifiers 38 a through 38 d without violating the performancerequirements parameters of the communication system (e.g. the errorvector magnitude parameters of a LTE communication system). Sinceperformance requirements parameters of a communication system are basedupon the communication signals input into the precoder 32, the excursioncompensation units 36 a, 36 b, 36 c, and 36 d compensate for excursionsafter the precoding.

For example, precoded communication signal 40 (whose magnitude isillustrated in FIG. 6A) may be output from precoder 32 into excursioncompensation unit 36 a and destined for amplifier 38 a. In the timedomain, an excursion magnitude portion 44 of precoded communicationsignal 40 which is greater than the signal magnitude threshold 42 ofamplifier 38 a may be extracted in the time domain (shown in FIG. 6B).The excursion portion consists of complex values corresponding tomagnitude values represented by time domain excursion magnitude portion44. Excursion magnitude portion 44 may have an example frequency domainprofile shown as frequency domain excursion signal 50 (as shown in FIG.7A).

Because excursion magnitude portion 44 has a value of zero in the timedomain for any time period that the magnitude of the precodedcommunication signal 40 is below the signal magnitude threshold 42 (asshown in FIGS. 6A and 6B), the associated frequency domain excursionmagnitude portion 50 will have a frequency spectrum larger than theoriginal bandwidth of the precoded communication signal 40. In otherwords, since there are portions of the excursion magnitude portion 44that are zero in the time domain, the frequency characteristics of theexcursion magnitude portion 50 may include sideband frequency noisecomponents that are outside of the original frequency domain bandwidthof the precoded communication signal 40. Accordingly, frequency domainexcursion signal 50 may be subjected to a bandpass filter to generatefrequency domain excursion signal 52 (shown in FIG. 7B) from frequencydomain excursion signal 50 which eliminates signals in frequencies thatwere outside of the original bandwidth of precoded communication signal40. The frequency spectrum of excursion signal 52 spans and correspondsto all of the frequency domain subchannels that were modulated inencoders/modulators 30 a and selectively mixed together by precoder 32,where the excursion magnitude portion 50 corresponded to time intervalswhere signal magnitudes were greater than the signal magnitudethresholds 42 of the associated amplifiers 38 a, 38 b, 38 c, or 38 d. Inembodiments, signal magnitude thresholds may be dynamic and/or may bedifferent for each of the amplifiers of the plurality of amplifiers.

The sideband frequencies which were filtered out from frequency domainexcursion signal 50 to generate frequency domain excursion signal 52 arenoise which should be eliminated from the communication system. Whenthis noise is filtered out by a bandpass filter, a portion of theoriginal signal power of excursion magnitude portion 44 is reduced. Inembodiments, time domain scaling of excursion signal 50 prior to mappingto the frequency domain may be implemented to accommodate for theattenuation due to the band pass filtering. In other embodiment, timedomain scaling may not be necessary if attenuation due to bandpassfiltering is accommodated in the frequency domain scaling of thesubchannels.

FIG. 7C illustrates frequency domain scaling of excursion signal 52 ofsubchannels 54 a through 54 h. Only eight subchannels 54 a through 54 hare illustrated for simplicity of explanation. However, communicationsystems may have tens or hundreds or thousands of subchannels, which aresometimes referred to as subcarriers by those of ordinary skill in theart. The frequency domain scaling of subchannels may be based on theprecoding parameters of that subchannel, the performance requirementsparameters of the communication signals input into precoder 32, and thepower levels of the subchannels input into precoder 32. The frequencydomain scaled excursion signals 54 a through 54 h may then be convertedback to the time domain into a complex waveform whose magnitude issubstantially similar to excursion magnitude waveform 44 (shown in FIG.6B). In other words, the frequency scaled excursion signal should havetime domain characteristics so that when excursion portion 44 issubtracted from the original signal 40, the magnitude of the resultingwaveform 46 is below the signal magnitude threshold 42 of an associatedamplifier.

The frequency domain scaled excursion signals 54 a through 54 h(illustrated in example FIG. 7C) should have frequency scaledcharacteristics which limit the frequency domain noise to permissiblelevels of a communication signal in accordance with performancerequirements parameters. At the same time, the time domaincharacteristics of the frequency scaled excursion signal 44 must havenoise distortions that when subtracted from the original signal 40 allowthe amplifier 38 a to operate below its magnitude signal threshold 42.Since the subchannels in the precoded communication signals are mixedtogether by precoder 32 of a MIMO communication system, each subchannelfor each precoded communication signal may be scaled to optimal orsubstantially optimal levels in order to ensure that the performancerequirements parameters are satisfied when the signals are reconstructedat the input to corresponding receiver demodulators, so that the amountof noise introduced does not exceed the performance requirementsparameters therein imposed. Embodiments relate to the frequency domainscaling of subchannels 54 a through 54 h such that performancerequirements parameters are satisfied and the scaled excursion signal 44subtracted from precoded communication signal 40 results in an excursioncompensated precoded communication signal that is below the signalmagnitude threshold 42 of the associated amplifiers 38 a through 38 d.

FIG. 7C illustrates an example scaled frequency domain subchannelsoutput from excursion compensation unit 36 a, in accordance withembodiments. Although only eight subchannels 54 a through 54 h areillustrated for simplicity, those skill in the art will appreciate thatany number of frequency distinguishable subchannels are possible (e.g.LTE communication systems can have thousands of subchannels). For thepurposes of illustration, subchannel 54 a may be at frequency ƒ₁,subchannel 54 b may be at frequency ƒ₂, subchannel 54 c may be atfrequency ƒ₃, subchannel 54 d may be at frequency ƒ₄, subchannel 54 emay be at frequency ƒ₅, subchannel 54 f may be at frequency ƒ₆,subchannel 54 g may be at frequency ƒ₇, and subchannel 54 h may be atfrequency ƒ₈. For simplicity of illustration, FIG. 7C only illustratesthe frequency domain scaling of multiple subchannels for one of theexcursion compensation units 36 a through 36 d.

Example FIGS. 8A through 8G illustrate a frequency domain scaling unitin relation to a zero padding unit and a tail compensation unit, inaccordance with embodiments.

Example FIG. 8A illustrates frequency domain scaling unit 60, inaccordance with embodiments. Extracted excursion signal 47 (whosemagnitude is illustrated as example waveform 44 in FIG. 6B) output fromexcursion extraction unit 58 may be input into frequency domain scalingunit 60. Extracted excursion signal 47 may be mapped to the frequencydomain in frequency domain mapping unit 72 to generate frequency domainexcursion signal 57 (illustrated as example frequency domain signal 50in FIG. 7A). In embodiments, frequency domain mapping unit 72 may use afast Fourier transform (FFT) or any other technique appreciated by thoseskilled in the art.

The frequency domain excursion signal 57 output from frequency domainmapping unit 72 may be input into subchannel scaling unit 76, inaccordance with embodiments. In embodiments, the subchannels in thefrequency domain excursion signal 61 (e.g. example subchannels 54 athrough 54 h illustrated in FIG. 7C) may be scaled according to theperformance requirements parameters of the communication system, thepower level of communication signals input into precoder 32, and theprecoding parameters used in precoder 32. The subchannel scaling unit 76introduces noise at levels that satisfy a communication system'sperformance requirements parameters in the respective subchannels intothe corresponding receiver demodulator, while eliminating the excursionin the time domain precoded communication signal 40 that is above thesignal magnitude threshold 42 (illustrated in example waveform 46 inFIG. 6C).

Frequency domain scaled subchannels 61 (illustrated as examplesubchannels 54 a through 54 h in FIG. 7C) are output from subchannelscaling unit 76. The frequency domain scaled subchannels 61 are mappedback to the time domain in time domain mapping unit 78 to generate atime domain channel scaled signal 49 having a substantially similarwaveform as the extracted excursion waveform 53 (whose magnitude isillustrated as example extracted signal 44 in FIG. 6B). The differencebetween extracted excursion waveform 53 and the time domain channelscaled signal 49 is that in the time domain channel scaled signal 49subchannel frequency components are scaled to satisfy the performancerequirements parameters of a communication system. The time domainchannel scaled signal 49 may be subtracted from the delayed firstprecoded communication signal 41 such that the associated amplifier 38operates below the signal magnitude threshold 42. In embodiments,mapping to the time domain using time domain mapping unit 78 may beperformed by an inverse fast Fourier transform (IFFT).

Example FIG. 8B illustrates zero padding unit 59 and tail compensationunit 67 disposed in relation to frequency domain scaling unit 60, inaccordance with embodiments. Signal 47 may be output from time domainexcursion generation unit 58 and may be coupled directly or indirectlyto zero padding unit 59, in accordance with embodiments. In embodiments,the output of zero padding unit 59 may be output directly or indirectlyto frequency domain scaling unit 60. In embodiments, the output offrequency domain scaling unit 60 may be output directly or indirectly totail compensation unit 67. Although (for illustrative purposes) exampleFIG. 8B illustrates signals directly between zero padding unit 59 andtail compensation unit 67, embodiments relate to signals beingindirectly communicated. For example, those skilled in the artappreciate that there may be other devices and/or components betweenzero padding unit 59, frequency domain scaling unit 60, and tailcompensation unit 67 without departing from the spirit or scope ofembodiments.

Example FIG. 8C illustrates frequency domain scaling unit 60, inaccordance with embodiments. Embodiments relate to frequency domainscaling unit 60 with frequency domain mapping unit 72 receiving a signaldirectly or indirectly from zero padding unit 72. Embodiments relate tofrequency domain scaling unit 60 with time domain mapping unit 78outputting a signal to tail compensation unit 67.

Example FIG. 8D illustrates K-point FFT 73 as a component of frequencydomain mapping unit 72 and K-point IFFT as a component of time domainmapping unit 78, in accordance with embodiments. In embodiments, K is aninteger equal to an integer power of two. Since fast Fourier transformsand inverse fast Fourier transforms are implemented most efficiently ondata frames having a length equal to an integer power of two, K may bean integer equal to an integer power of two, in accordance withembodiments.

Example FIG. 8E illustrates illustrates 2L-point FFT 73 as a componentof frequency domain mapping unit 72 and 2L-point IFFT as a component oftime domain mapping unit 78, in accordance with embodiments. L may be aninteger power of two which is implemented in FFT or IFFT operations ofencoder/modulator 30. Given that the addition of a cyclic prefix (insome embodiments) adds a length less than L, then the FFT and IFFT infrequency domain scaling unit 60 may be exactly twice the length (e.g.2L) of the FFT and IFFT lengths in encoder/modulator 30. In other words,K=2×L, in accordance with embodiments.

Example FIG. 8F illustrates zero padding unit 59, in accordance withembodiments. In embodiments, signal 47 from time domain excursiongeneration unit 58 may be directly or indirectly received by zeropadding unit 59. In embodiments, excursion receiving unit 75 may receivesignal 47 have a frame length of N. N may be the length of the frame(e.g. L) output from encoder/modulator 30 plus any length added bycyclic prefix unit 33, in accordance with embodiments. N may be aninteger that is not equal to a power of two. According, based on thelength of N, zero pad generator 79 may append zero or nominal values N+1to K such that the frame length input into zero padding appending unit77 has K inputs and K is an integer power of two, in accordance withembodiments. In embodiments, zero padding appending unit 77 may output Koutputs (e.g. 47(N) through 47(K) to frequency domain scaling unit 60.Since K is an integer power of two, the signal input into frequencydomain scaling unit 60 can implement efficient FFT and IFFTcomputations, in accordance with embodiments. Those skilled in the artappreciate other implementations of zero padding unit 59 that aredifferent from that illustrated in example FIG. 8F that do not departfrom the spirit and scope of embodiments. In other words, FIG. 8Fillustrates just one example implementation of the embodiments.

Example FIG. 8G illustrates tail compensation unit 67, in accordancewith embodiments. In embodiments, frequency domain scaling unit 60outputs a signal having a frame length K. This signal is input into atleast two buffers (e.g. buffer 84 a and buffer 84 n). Buffer 84 aoutputs a signal 86 a to tail extraction unit 88 and buffer 84 n outputssignal 86 n to tail extraction unit 88, in accordance with embodiments.Since the original signal input into zero padding unit 59 had a length N(which may not be an integer power of two), tail extraction unit 88 maydiscard data in frames N+1 to K in order to produce a signal having thesame frame length as that input into zero padding unit 59, in accordancewith embodiments. Since the signal output from tail compensation unit 67will ultimately be subtracted from an original signal (e.g. D41), tailextraction unit 88 discards the excess data in a frame that waspreviously added for computational efficiency of frequency domainscaling unit 60, in accordance with embodiments. Those skilled in theart appreciate other implementations of tail compensation unit 88 thatare different from that illustrated in example FIG. 8G that do notdepart from the spirit and scope of embodiments. In other words, FIG. 8Gillustrates just one example implementation of the embodiments.

Example FIGS. 9A through 9H illustrate a frequency domain scaling unitin relation to an interpolation unit and a decimation unit, inaccordance with embodiments.

Example FIGS. 9A and 9B illustrate interpolation unit 63 and decimationunit 65 receiving feedback from cyclic prefix unit 31, in accordancewith embodiments. In embodiments, in order to implement efficient FFTand IFFT processing in frequency domain scaling unit 60, interpolationunit 63 may sample signal 47 at a rate that outputs a frame having adata length that is an integer power of two. A sample rate ofinterpolation unit 63 may be variable and may be a factor of both thelength of the original frame and the length of the added cyclic prefix.Likewise, decimation unit 65 should decimate the signal output fromfrequency domain scaling unit 60 so that the signal 49 output fromdecimation unit 65 has the same frame length as signal 47 input intointerpolation unit 63. Those skilled in the art appreciate otherimplementations may be different from that illustrated in example FIGS.9A and 9B that do not depart from the spirit and scope of embodiments.In other words, FIGS. 9A and 9B illustrate just one exampleimplementation of the embodiments.

Example FIGS. 9C and 9D illustrate that frequency domain scaling unit 60may include a K-point FFT 73 and K-point IFFT 79, in accordance withembodiments. K may be an integer that is an integer power of two, inaccordance with embodiments. In embodiments, K-point FFT 73 and K-pointIFFT 79 may be 2L-point FFT 73 and 2L-point IFFT 79, such that thelength of a data frame processed by frequency domain scaling unit is aninteger multiple (e.g. 2L) of the length of the FFT and/or IFFTprocessing length in encoder/decoder 30. FIGS. 9C and 9D illustrate justone example implementation of the embodiments.

Example FIGS. 9E and 9F illustrate interpolation unit 63 withinterpolation calculation unit 92 and adjustable interpolator 90, inaccordance with embodiments. Signal 47 may be received by interpolationunit 63 from time domain excursion generation unit 58. Since signal 47may have a cyclic prefix added, signal 47 may have a frame length thatis not an integer power of two. Interpolation calculation unit 92 mayreceive feedback from cyclic prefix unit 31 as to the length of thecyclic prefix and calculate the rate of interpolation needed to generatesignals 47(A) through 47(K) that have a length that is an integer powerof two, such that these signals can be efficiently processed byfrequency domain scaling unit 60. An output of interpolation calculationunit 92 may be output to adjustable interpolator 90, which adjusts theinterpolation rate to generate a data frame having a length that is aninteger power of two. In embodiments illustrated in FIG. 9F, adjustableinterpolation unit 90 output signals 47(A) to 47(2L) such that the datalength is exactly twice the length of the FFT and/or IFFT processinglength in encoder/decoder 32. FIGS. 9E and 9F illustrate just oneexample implementation of the embodiments. In embodiments, interpolationcalculation unit 63 may calculate the interpolation rate as a valueK/(L+N) times the sampling rate of the received communication signal.

Example FIGS. 9G and 9H illustrate decimation unit 65 with decimationcalculation unit 96 and adjustable decimator 94, in accordance withembodiments. Signals 47(A) through 47(K) may be received by decimationunit 65 from frequency domain scaling unit 60. Decimation calculationunit 96 may receive feedback from cyclic prefix unit 31 as to the lengthof the cyclic prefix and calculate the rate of decimation needed togenerate signal 49 that has a frame length equal to that input intointerpolation unit 63. An output of decimation calculation unit 96 maybe output to adjustable decimator 94, which adjusts the decimation rateto generate a data frame that has a frame length equal to that inputinto interpolation unit 63. In embodiments illustrated in FIG. 9H,adjustable decimator unit 94 outputs signal 49 by decimating signals47(A) to 47(2L) such that the data length is exactly twice the length ofthe FFT and/or IFFT processing length in encoder/decoder 32. FIGS. 9Gand 9H illustrate just one example implementation of the embodiments. Inembodiments, decimation unit 65 may calculate the decimation rate as avalue (L+N)/K times the sampling rate of the received communicationsignal and/or the inverse proportion of the interpolation ratecalculated by interpolation unit 63.

Although embodiments and their advantages have been described in detail,it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the disclosed as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, compositionof matter, means, methods and steps described in the specification. Asone of ordinary skill in the art will readily appreciate from thedisclosure of the present invention, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the present invention.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps.

1. A method comprising: receiving a communication signal; splitting thecommunication signal into a first communication signal and a secondcommunication signal; zero padding the first communication signal; andexcursion compensating the first communication signal with the secondsignal to generate an excursion compensated signal. 2-56. (canceled)